1. Field of the Invention
The present invention relates to a composite sliding material applicable to bearings and so on.
2. Brief description of the Art
JP-A-10-212534 (which is a Japanese patent application filed by the same assignee) discloses a composite sliding material, as shown in FIG. 3, which consists of a back metal 1, a porous alloy layer 2 and a resin layer 3, wherein the porous alloy layer is formed on the surface of the back metal by sintering an alloy powder and the resin layer is formed so as to impregnate into and cover the porous alloy layer. The alloy layer 2 is provided on the back metal 1 in order to firmly bond the resin layer 3 to the back metal since the resin layer is not strongly bonded to the back metal. The alloy layer consists of sintered alloy particles having an average particle size of 125 xcexcm and has a thickness of superimposed about three alloy particles.
Whereas, recently, a composite material, of the same type as stated above but having smaller sliding-contact resistance, has been required. Under such a requirement, the inventors noted that there is a significant relationship between a degree of the sliding-contact resistance and a recession depth of the resin layer resulted from deformation by a load exerted on the resin layer, and examined a sliding material with a resin-layer filled with a hard material. However, the hard material is liable to attack the mating member. Although it is possible to reduce the deformation degree or the recession depth of the resin layer by making the resin layer thin, the alloy layer is liable to be exposed due to a small wear loss of the thin resin layer, whereby a problem of durability arises.
On the other hand, the inventors found by trial and error that the recession depth of the resin layer resulted from deformation under loading is affected also by elastic deformation of the alloy layer. However, taking this finding into consideration, if the number of superimposed alloy particles is reduced, bonding strength of the resin layer to the back metal is decreased resulting in that a separation may occur.
Accordingly, an object of the present invention is to provide a composite sliding material comprising a back metal, a porous alloy layer which is formed on the surface of the back metal by sintering an alloy powder, and a resin layer which is formed so as to impregnate into and cover the porous alloy layer, which has a lower sliding-contact resistance, while ensuring enough bonding strength of the resin layer to the back metal, by making alloy particles constituting the alloy layer to have a smaller particle size.
According to a key aspect of the invention, there is provided a composite sliding material comprising a back metal, a porous alloy layer which is formed on the surface of the back metal by sintering a copper alloy powder, and a resin layer which is formed so as to impregnate into and cover the porous alloy layer, wherein the copper alloy powder has an average particle size of 25 to 100 xcexcm, and the alloy layer, consisting of sintered copper alloy particles, has a thickness of superimposed plural particles.
According to an application manner of the composite sliding material, such as a wet or dry condition of operation, optionally the resin layer may be thermoplastics including fluorocarbon polymer (such as PTFE), polyacetal (such as POM) and aromatic polyether ketone (such as PEEK); thermosetting resin including phenol and polyimide; an admixture thereof; or any one of these into which graphite or molybdenum sulfide (MoS2) is added.
The copper alloy constituting the alloy layer may comprise typically Sn, P or Pb. Since a much amount of Sn makes the alloy layer hard, Sn is limited to an amount range of 6 to 15 mass %, desirably 8 to 12 mass %. Regarding P (phosphorus), it is desirably added into the copper alloy in order to improve sintering capability. But, since a much amount of P makes the alloy layer hard to have high attack property against the mating member, the amount of P is limited to less than 0.6 mass %. Regarding Pb, in the case where the composite sliding material is used under a wet condition, 3 to 12 mass % of additive Pb improves sliding-contact property of the material. Thus, the additive alloying elements may be optionally selected as a combination thereof or a single element taking an application manner of the material into consideration.
While the alloy layer is formed to be porous by sintering the copper alloy powder, if the porosity thereof is small, the amount of resin impregnation into the porous alloy layer becomes smaller resulting in separation of the resin layer from the alloy layer. Thus, the alloy layer has desirably a porosity of not less than 20%.
The smaller the average particle size of the copper alloy particles constituting the alloy layer is, the smaller the sliding-contact resistance becomes. Taking this into consideration, the average particle size is limited to a range of 25 to 100 xcexcm. The lower limit is set because, if the average particle size is less than 25 xcexcm, the bonding strength of the resin layer to the alloy layer is inferior.
Further, with respect to the thickness of superimposed alloy particles or the number of superimposed alloy particles which constitute the alloy layer, the smaller the number is, the smaller the sliding-contact resistance becomes. But, if the number is xe2x80x9c1xe2x80x9d, the bonding strength of the resin layer to the alloy layer is inadequate leading to liability to separation of the both layers, and the composite sliding material will have high attack property against the mating member. Thus, the alloy layer is defined to have a thickness of superimposed plural alloy particles. Preferably, the alloy particles are superimposed in the thickness direction by the particle number of 2 to 4 taking the sliding-contact resistance into consideration. Although the respective alloy particles has desirably a spherical form, it may have other forms.
As defined in claim 1, the composite sliding material comprises a back metal, a porous alloy layer which is formed on the surface of the back metal by sintering a copper alloy powder, and a resin layer which is formed so as to impregnate into and cover the porous alloy layer, wherein the copper alloy powder has an average particle size of 25 to 100 xcexcm; and the alloy layer, consisting of sintered copper alloy particles, has a thickness of superimposed plural particles, whereby it does not so damage the mating member and has a smaller sliding-contact resistance.